1. Field of the Invention
The present invention relates generally to isolation valves disposed in commercial and industrial fluid transport systems, and more particularly to an apparatus and method for simply and economically detecting leaky valve seals and defective fluid flow diverters without interrupting fluid transport system operations.
2. Background of the Invention
In many commercial and industrial fluid transport systems, isolation valves are employed as a defense against the development and escalation of hazardous operating conditions. As a result of their simple design, isolation valves are generally maintained in either an open or closed position for the majority of their operational lives; the particular operational position is primarily dependant upon the process environment in which the valves are employed. Unlike more sophisticated modulating control valves, which can be monitored and diagnosed for fluid leakage by periodically comparing the valve position and a fluid path flow rate, isolation valves have primarily been monitored and diagnosed in the past using one of the following previously known methods.
First, high frequency acoustical systems can be used to identify leaky valves under certain conditions. For example, valve leaks can be detected using high frequency acoustics when a monitored isolation valve is set in a closed position and a significant pressure gradient exists within the valve along the directional axis of the flow path. One or more pressure sensors are then used to “listen” for high frequency noise created by valve leakage.
One drawback to such a configuration is that, since the valve must first be completely closed in order to monitor or diagnose fluid leakage, the entire system must be taken off-line for monitoring and diagnosis activities. Moreover, since a significant pressure gradient must exist across the valve in order for a leak to be detected by the sensors, minor leaks may go undetected for a period and only later become apparent, perhaps after a significant escalation of a hazardous process condition has already occurred, or even after the valve seals have completely failed. Also, since valves in which only one of several seals has failed will not generally exhibit a significant pressure gradient along the flow path, partially leaky valves can also go undetected for some time. Finally, such tests can fail to detect whether the valve's fluid flow diversion means is functioning properly, since most valves are permanently disposed in only a single operational position during operations (i.e., either open or closed). In cases where the test is carried out on a valve that is operated in a continuously closed position, there is no way to discern whether the fluid diverter could in fact be opened during an emergency situation.
As seen in U.S. Pat. No. 6,128,946 to Leon et al., detection of leaky valve seals may also be accomplished using a system in which a series of pulsations caused by fluid vibrations within the transport system are compared to pulsations occurring within a valve's inner cavity as a function of time. Such configurations require at least two pressure sensors, one located within the system's flow path either upstream or downstream relative to the valve, and another disposed within the valve's inner cavity. The pulsations measured by the sensors can then be used to determine whether the pulsations detected within the transport system are being passed into the valve's inner cavity, thereby revealing the presence of leaky seals within the valve.
However, since the system of Leon et al. also requires, at minimum, a plurality of transducers, an analyzer to perform pulsation comparisons, and an appropriate transport system process connection disposed relatively close to the valve in order to function effectively, those of ordinary skill in the art have found the configuration to be unnecessarily cumbersome and expensive, and of limited application in transport systems having a complex geometry.
Finally, leaky valves may be detected when applying an external pressure source directly to the isolation valve's inner cavity by measuring the rate at which fluid leaks into the valve, and then comparing the results to a table of predetermined parameters and assessing the integrity of the seals. Those of skill in the art have also found this approach dissatisfactory, however, because the fluid transport system must first be taken off-line to perform testing and maintenance (since internal process pressures on the valve must be interrupted to determine whether the seals are allowing fluid to leak back into the valve), and both an external source of pressure and additional operational personnel are required.
In view of the foregoing, it is apparent there is a widespread need for a method and apparatus for simply and economically detecting leaky valve seals and defective flow diverters while an associated fluid transport system continues to operate on-line.